1. Field of the Invention
The present invention relates to a fuel cell catalyst, a membrane-electrode assembly including the fuel cell catalyst, and a fuel cell in which at least one of a cathode electrode and an anode electrode includes the fuel cell catalyst.
2. Description of the Related Art
A fuel cell electrochemically oxidizes fuel such as hydrogen or methanol in the cell, thereby directly converting the chemical energy of the fuel into electrical energy and extracting this electrical energy. Since neither NOX nor SOX is produced by combustion of fuel, unlike in a thermal power station, a fuel cell has attracted attention as a clean electrical energy supply source. In particular, a polymer electrolyte fuel cell can be made smaller and lighter than other fuel cells and hence has been developed as a spacecraft power feed. Recently, polymer electrolyte fuel cells are also extensively studied as power supplies for automobiles.
As the electrode structure of a fuel cell, a five-layered structure made up of cathode collector/cathode/proton conductive film/anode/anode collector is known. What is particularly important in the formation of the anode electrode and cathode electrode is to prevent toxication of the electrodes by carbon monoxide or the like and raise the activity per unit catalyst. To avoid toxication and raise the activity, it is conventionally attempted to select a catalyst metal to be supported, and carry this catalyst metal in the form of a metal or an alloy, to produce high-performance fuel cell catalysts and electrodes. The particle size of an alloy or the like is also studied, and a particle size of a few nm is regarded as appropriate.
In a fuel cell catalyst, carbon is generally used as support for supporting a catalyst support. This is because carbon is conductive, electrons generated on the carbon support surface can be extracted, and it is presumably effective to directly adhere the catalyst metal to the carbon support.
Unfortunately, a carbon supported catalyst obtained by supporting platinum or a platinum alloy on a carbon support is inferior in cell performance, such as the voltage characteristic.